Proteins have long been postulated to have semiconductor properties. Using proteins as a semiconductor would be exciting due to their ready availability and the possibility of forming them in a very thin (e.g. monomolecular or bi-molecular) layer. However, the electrical properties of such proteins have proven very difficult to measure due to the very properties of proteins which make them exciting.
Specifically, it is very difficult to apply a current across a monomolecular protein layer and measure its characteristics. Prior to the present invention, there has been no stable way, therefore, of applying current to a protein and measuring its semiconductor characteristics.
One previous attempt to measure the semiconductor characteristics of protein within the personal knowledge of the inventor of this invention has used microscopic samples of dried protein. This attempt has detected virtually no conduction. Another attempt used proteins adsorbed on a single metal surface immersed in a solution. The current in this solution was carried by the reduction of a hydrogen ion and was, therefore, not purely electronic. These two attempts have therefore proved severely deficient.
Another attempt can be found in U.S. Pat. No. 4,902,555. This technique uses proteins in a protein transport situation where it can accept and donate electrons. The inventors of '555 stated that they used the electron transfer proteins from an organism to provide a transistor characteristic. However, they totally ignored the metal/protein junction in their device. This junction has proved to be one of the most difficult to properly fabricate, and is a main advantage of the present invention. It is doubtful whether this device could actually work because any roughness in the metal would be expected to pierce the protein layer. The FIG. 6 embodiment used metal electrodes of silver, gold or aluminum, and placed the electron transfer protein on the substrate.
The '555 patent teaches that the film of protein molecules is formed according to a Langmuir Blodgett technique, but there is no suggestion as to how this protein layer would be connected. Moreover, the way in which an aqueous environment would be maintained is at best speculative.
Other techniques have been used to form semiconductor devices in liquid environments. For instance, U.S. Pat. No. 2,734,154, teaches a semiconductor material where the conducting metal used to conduct current to and from the semiconductor is mercury. There is nothing, however, teaching that this could be used in combination with any protein.
The present invention is intended to obviate all of these problems, and defines a semiconductor device and method of forming and testing such a semiconductor device which uses protein as its active element. The device includes a containing structure which contains a liquid, with first and second liquid metal electrode drops within the space. A protein layer is adsorbed to at least one of the liquid metal electrodes, and sandwiched therebetween. An electrically connecting means connects to the first an second liquid metal electrode drops. The metal preferably includes mercury, and the electrodes are preferably in contact with and bounded by the interior walls. The container is preferably a tubing which is bent into a "U-shape" to contain the liquid in a center portion thereof.
A similar technique is also disclosed for forming a semiconductor test set which uses a protein-containing semiconductor device as discussed above, and a test set which applies a signal between the electrodes and measures a response. A method of making such a semiconductor is also disclosed. This method includes filling an open end container with a biological protein and inserting first and second liquid metal electrodes of a type to which the biological protein will adsorb into the container. The first and second electrodes are positioned adjacent one another with a biological protein therebetween and adsorbed to at least one of the electrodes. A method of testing such a biological semiconductor is similarly disclosed.